1. Field of the Invention
This invention generally relates to thermostatic devices which measure temperature inside a building and starts or stops a heating system. The control described herein adjusts the temperature set point as a function time of day, and more specifically, the economical heating of a space using temperature setback. The present invention further varies the rate of set point rise during a warm up period.
2. Description of Prior Art
Because of high energy costs it is desirable to run environmental heating systems with reduced night time temperatures in a space. Thus, thermostats are setback to lower temperatures at night or unoccupied periods to reduce heat losses from the building. This practice is well known and is documented in reports such as U.S. Government, #EDM-1023(1-77), "Energy Savings through Automatic Thermostat Controls" which show that a 10.degree. F. night time temperature setback can save as much as 15% of annual energy consumption. Thermostats now available can provide the mechanism for the setback control but they have two major disadvantages, which are;
(a) Thermostats are usually set to bring up the temperature in a space at a fixed time; often at a time sufficient to provide warm up for the coldest expected outside temperature. Thus, unnecessarily long periods of high space temperatures (t.sub.r) result in normal building operation. PA1 (b) Heating systems such as heat pumps use energy to transfer heat contained in the outside air to the inside of a structure. Heat pumps are characterized by the ability to transfer or pump more energy into the building than it takes to run the heat pump system. However, heat pumps have capacity problems due to their size or low ambient temperature and are therefore equipped with 2nd stage heaters, usually electric resistant type. These secondary electric heaters have a low coefficient of performance where only the energy used by the heaters is delivered into the space. Thus, when using a normal setback type thermostat and when the space has cooled due to setback, a normal control's large temperature setting change will often initiate both the heat pump and the second stage resistant heaters resulting in high operating costs. Temperature setback then may not save energy costs because of the operation of second stage heaters. Manufacturers of heat pumps in fact, advise users not to use nignt setback, --see "Energy Saving Through Thermostat Setback with Residential Heat Pumps" by C. E. Bulluck, ASHRAE TRANSACTION 1978.
Overall energy conservation and lower operating costs can be achieved in heating systems using temperature setback if the thermostatic set point temperature is adjusted to start a heating system at a time sufficiently early to allow the proper warm up of a space to a time/temperature target but without using secondary heating units. Various patents have been granted that allow optimum time start operation such as U.S. Pat. Nos. 3979059 and 4106690. Also some sophisticated marketed computerized systems such as the Johnson JC-80 Control System or the Robertshaw Model #SST-8801 Optimizer have been marketed that will establish a calculated start time based on outside temperatures. These devices and patents are electronic/mechanical and are costly and complex.